Copper with good conductivity has conventionally been used for the substrate of conductive members such as busbars. Recently, aluminum or aluminum alloys are often used for various reasons, such as soaring copper prices. However, films of insulating oxides and hydrates easily form on the surface of aluminum or aluminum alloys, and an increase in contact resistance over time has been a problem. Thus, to improve conductivity for a conductive member using a substrate comprising aluminum or an aluminum alloy, a Sn plating layer is provided on contact parts for conducting electricity to members to be conducted.
Aluminum or aluminum alloys are materials that are difficult to plate when a Sn plating layer is provided, and thus, the surface thereof is first zincate-processed and a Zn layer is provided. The Zn layer may dissolve in some cases due to a Sn plating bath, which is a strong acidic bath. Thus, a Ni plating layer formable by a weak acidic bath is usually further provided as an underlayer on the Zn layer, and a Sn plating layer is provided on the Ni plating layer (Patent Documents 1 and 2).    [Patent Document 1] JP 2013-227630 A    [Patent Document 2] JP 2006-291340 A